%%
%% The LaTeX Companion, 3ed
%%
%% Example 9-7-3 on page I-739 in "Substituting the font family if unavailable in an encoding".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{87.0pt}

%  \setlength\parindent{0pt}

%StartShownPreambleCommands
\usepackage[greek,english]{babel}
\DeclareFontFamilySubstitution{LGR}{Montserrat-LF}{IBMPlexSans-TLF}
%StopShownPreambleCommands

\begin{document}
\fontfamily{Montserrat-LF}\selectfont
The root of \TeX\ is \foreignlanguage{greek}{τεχνική}.
\end{document}
